Mass measurements of neutron-rich nuclei constrain element abundances

中性子過剰な質量数90領域原子核の質量測定が元素存在比を制限する

Xian, W.*; 伊藤 由太   ; 他30名*

Xian, W.*; Ito, Yuta; 30 of others*

Atomic masses of the neutron-rich isotopes Ga, Ge, As, Se, Br, Kr, and Rb have been measured with high precision and accuracy using the multi-reflection time-of-flight mass spectrograph at the RIBF facility. The masses of As were measured for the first time and the mass uncertainties of Ge and Se were significantly reduced from several hundred keV to below the 10 keV scale. Investigation of shell evolution and potential subshell closures are proceeded by analysis of two-neutron separation energy systematics. As a result of the precise mass measurements, no prominent change on the slope of the two-neutron separation energy beyond is observed in Se isotopes, indicating the subshell closure effect at of Se does not exist. Also, various leading mass models are compared with the measurements. The impact of the more precisely known data on r-process nucleosynthesis calculations is investigated in light of these new mass measurements, showing a remarkable reduction of reaction-rate uncertainties.